Pressure sensitive adhesives have for a long time been used for attaching medical devices, such as ostomy appliances, dressings (including wound dressings), wound drainage bandages, devices for collecting urine, orthoses and prostheses to the skin.
Hydrocolloid adhesives containing hydrophilic particles or absorbents, which absorb moisture into the adhesive bulk and transmit moisture when conditions are saturated, are one well-known group of pressure sensitive adhesives useful for attaching medical devices to the skin. However, the retention of moisture in hydrocolloid adhesives may cause changes in the adhesive, such as swelling, loss of cohesion and disintegration. Non-absorbing adhesives on the other hand, may trap excessive moisture between the skin and adhesive, causing weakening of adhesion and maceration of the skin.
Due to the delicate nature of skin, there is a narrow window where a pressure sensitive adhesive can function as a good and skin friendly adhesive: On one hand, the adhesive should be able to attach the medical device to the skin and the device should not fall of during wear and on the other hand, removal of the medical device from the skin should not cause damage to the skin.
For medical uses, a high water vapour transmission through the pressure sensitive adhesive is desirable. However, the availability of pressure sensitive adhesives with high water vapour transmission, which are suitable for skin contact use, is limited.
The water vapour transmitting pressure sensitive adhesives currently used for adhesion to the skin are mainly silicone, PU and acrylic based adhesives.
Pressure sensitive adhesives based on acrylics are usually solvent based and may include toxic residues and monomers causing malodour. These adhesives may incorporate hydrophilic components, such as hydrocolloids, which absorb moisture. However, the content of hydrophilic components and hence the absorption of moisture changes the properties of the adhesive, swelling and reduced adhesion being the most undesirable effects. The wear time of such acrylic adhesives is typically short due to these effects.
Silicone adhesives are relatively expensive and have a relatively low moisture transmission, which causes problems with regard to breathability. Adhesion may also be compromised, when moisture builds up between the skin and the adhesive. Moreover, the compatibility of silicones with other organic materials (e.g. polymers) is limited, which affects the blending stability with performance enhancing additives, and adhesion to reinforcement materials of another chemical composition.
Pressure sensitive adhesives based on silicone or polyurethane are typically thermoset materials that undergo an irreversible cross-linking reaction during processing.
Adhesives based on apolar polymers like SIS and PIB are well known in the technical field of medical adhesives. E.g. WO 99/11302 describing adhesives for medical use based on SIS, PIB and hydrocolloids and U.S. Pat. No. 4,551,490 describing adhesives containing SIS/SI, PIB/butyl rubber, tackifier, mineral oil and hydrocolloids.
Ethylene copolymers are often used in hot-melt adhesives for e.g. packaging and labels. The EVAs used for these purposes are the traditional EVA types containing up to 40% vinyl acetate, i.e. the polymer is relatively apolar.
Adhesives containing EVA with more than 40% vinyl acetate are also described.
U.S. Pat. No. 4,477,325 describes a skin barrier composition made of EVA, PIB and water absorbing particles or polymers. The EVA may contain from 25 to 65% by weight of vinyl acetate.
U.S. Pat. No. 6,933,342 describes a formulation comprising a triblock copolymer (styrene-diene-styrene), a terpene resin, a liquid and EVA polymer wherein the EVA polymer preferably possess a vinyl acetate content of more than 50% by weight.
U.S. Pat. No. 6,225,520 describes an adhesive containing ethylene copolymer as e.g. EVA, solid tackifier resin, liquid tackifier resin, antioxidant and optionally a diluent. The EVA polymer exhibiting a vinyl acetate content of between 15 and 65% by weight. The invention relates to adhesives for labels and tapes, including tapes for skin contact.
The adhesive described above all have the drawback that they contain apolar components, which result in an adhesive matrix (adhesive without hydrocolloids) with no or low water permeability. If the adhesive has to be used for skin contact, they need to be able to handle moisture. When the types of materials described above are used as skin adhesives, a large amount of absorbing particles are often added to handle the moisture.
The addition of particles in large amounts results in a relatively hard adhesive material, which has reduced tack and weak durability and often leads to skin stripping. To avoid this kind of skin damage, it can be an advantage to use a permeable adhesive material that can handle the moisture developed at the skin surface. Hereby no or a low amount of hydrocolloids needs to be added.
It has been found that pressure sensitive adhesives based on polar ethylene copolymers and polar oil or a combination of polar oils provides an excellent skin adhesive.
These adhesives also have a very high moisture vapour transmission rate, which makes them breathable and very skin friendly. The high moisture transmission of these adhesives is a particular advantage where a medical device has to be worn on the skin for a long time, e.g. days.
It has surprisingly been found, that the adhesives according to the invention provide softness, flexibility, safety and comfort in wear, a low toxicity compared with acrylic adhesives and a good moisture transmission compared to silicon adhesives.